Root-knot nematodes are considered as one of the most economically damaging of plant-parasitic nematodes of tomato. In many cases, crop losses due root-knot nematodes are reduced by the application of high toxic chemical nematicides. In Ghana, farmers’ management practices against root-knot nematodes are in most cases ineffective. The purposes of the study were to determine farmers’ perception of root-knot nematodes, evaluate the efficacy of organic amendments at the laboratory, plant house and field,assess the effect of fresh sweet orange and cassava combination on root-knot nematode isolates, confirm the presence of the nematodes (Meloidogyne spp.) using ITS-PCR molecular analysis,determine the time of application and appropriate rate for the management of the nematodes on tomato. In determining farmers’ perception of root-knot nematodes and their management methods, multistage sampling technique was used to select the respondents. The survey was carried out in six district in Ashanti region. Majority (30%) of the tomato farmers were aware of root-knot nematode problems in their fields. Majority of them identified root-knot nematodes as the most prevalent pest in tomato. However, none of them used nematicides in the management of the nematodes. All the farmers used crop rotation and weeding as a management strategy against the nematodes. For the evaluation of the efficacy of organic amendments in the management of the nematodes, experiments were carried out in the laboratory, plant house and research field of KNUST. In the laboratory, fresh sweet orange peels significantly (P<0.05) inhibited egg hatching and increased mortality of root-knot nematodes than the rest of the treatments. Fresh orange peel performed just as well as carbofuran in reducing the number of root-knot nematodes in the root of tomato and soil, number of eggs, root galling and reproduction factor of the nematodes in the plant house. In the field, the application of fresh sweet orange peels followed by cassava peels and the reverse application of the two materials significantly increased (P<0.05) the fresh shoot weight, fruit size and yield of tomato than the other treatments. The number of root-knot nematodes in the roots of tomato and soil, number of eggs and root galling were significantly reduced (P<0.0) upon the application of carbofuran and its effect was similar to that of the combined application of fresh sweet orange and cassava peels. The application of sweet orange peels significantly increased (P<0.05) the number of colonies of Trichoderma viride than cassava peels, but cassava peels also significantly increased (P<0.05) the number of the bacterivorous nematodes,Heterocephalobellus sp. andEucephalobus sp. and the fungivorous nematodeDitylenchussp.more than sweet orange peels. Further evaluation of the combined application of fresh sweet orange and cassava peels on root-knot nematode isolates showed no significant differences (P>0.05) between the isolates in terms of number of juveniles in the roots of tomato and soil, number of eggs, root galling and reproduction factor. However, the pots treated with combined application of fresh sweet orange and cassava peels significantly increased (P<0.05) the fresh shoot weight and plant height of tomato more than carbofuran-treated pots. The amplification of the ITS regions of the nematodes, using multigene loci primers, confirmed the presence of Meloidogyne spp. The application of fresh sweet orange and cassava peels combination at four weeks before transplanting significantly reduced (P<0.05) the population of root-knot nematodes and root galling of tomato than the rest of the treatments. Similarly, the application of 25g each of both fresh sweet orange and cassava peels per pot significantly reduced (P<0.05) the nematode population and root galling and inceased fresh shoot weight and yield of tomato than the other treatments. The study showed that root-knot nematode infestation was one of the major problems of tomato farmers and there was no effective management technique. The combined application of fresh sweet orange and cassava peels at 50g/plant four weeks before transplanting was found to be the most effective treatment in the management of the nematodes. The nematode isolates collected from different tomato growings areas were confirmed to be Meloidogyne spp. Therefore, further evaluation on the efficacy, time and rate of application of fresh sweet orange and cassava peels combination is recommended. Also, simple and more reliable method such as isozymes should be used to identify root-knot nematodes to the species level.

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A thesis submitted to the Department of Crop and Soil Sciences. Kwame Nkrumah University of Science and Technology in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Nematology, 2016